(maint) Replace file utility functions with Boost file_system.

Adding Boost file_system to the build. This is a better cross-platform library for file system abstractions.
(CFACT-26) Add block device facts for Linux.

Implementing the following facts for Linux:

- blockdevice_<device>_size
- blockdevice_<device>_vendor
- blockdevice_<device>_model
- blockdevices
Merge pull request #22 from peterhuene/facts/blockdevice

(CFACT-26) Add block device facts for Linux.